This invention relates to an expanding headpiece for reels in general.
For many industrial applications where a sheet or web element is to be wound and unwound on/from a reel, it is known to utilize expanding headpieces which are inserted into the reel core to function as rotary motion supports.
Considering the particular field of pneumatic action expanding headpieces, a headpiece is disclosed in U.S. Pat. No. 3,108,757 which comprises a cylindrical body which is secured to its rotary shaft by means of clamps or jaws and has on its external surface an annular receptacle accommodating an annular chamber therein, which annular chamber is formed from an elastically deformable material and can be expanded radially by pneumatic action such as to make the headpiece rigid with the interior of the core of a reel.
That approach, while affording the advantage of automatically accommodating any play which may develop in the course of the rotary operating steps, has the disadvantage of being non-selfcentering, in that the applied weight load of the reel, owing to the rotation axis being horizontal, unavoidably induces a degree of eccentricity in the deformation of the membrane or elastic annular chamber, with consequent eccentric rotation of the reel as a whole, which may result in a number of problems, especially where high winding and unwinding speeds are used, and hence produces vibration of considerable magnitude.
In an effort to remove such a drawback, the outside surface dimensions of the cited headpiece type are selected to be as close as possible to the inside diameter dimensions of the reel core, so as to minimize play; of course, this expedient can only be palliative, because the reel inside diameters differ, however slightly, between reels and it is unthinkable of providing a number of headpieces for each reel to obtain accurately fitting dimensions.
U.S. Pat. No. 3,097,808 discloses an expanding headpiece which can be engaged with the axial ends of the reel core in so-called "shaft-less" systems, wherein to make the headpiece self-centering, said headpiece again comprising a pneumatically deformable elastic material annular chamber as an expansion member, at the side connection flange a frustoconical surface is provided which, when inserted into the core and, acts as a self-centering support or bearing member. However, the contact area between the frustoconical surface and reel end is in this case generally quite small, and the deformations unavoidably undergone by the reel core during the operating steps create plays which result in the reel being liable to take a less than perfectly centered attitude relatively to its rotation axis.